Because of the searchmechanism for unique key constraints on multiple columns, you cannot haveidentical values in the non-null columns of a partially null composite uniquekey constraint. 二. 相关测试 2.1 测试unique index 和 uniqueconstraint SYS@anqing2(rac2)> create table ut(idnumber,phone varchar...
Because of the searchmechanism for unique key constraints on multiple columns, you cannot haveidentical values in the non-null columns of a partially null composite uniquekey constraint. 二. 相关测试 2.1 测试unique index 和 uniqueconstraint SYS@anqing2(rac2)> create table ut(idnumber,phone varch...
Because of the searchmechanism for unique key constraints on multiple columns, you cannot haveidentical values in the non-null columns of a partially null composite uniquekey constraint. 二. 相关测试 2.1 测试unique index 和 uniqueconstraint SYS@anqing2(rac2)> create table ut(idnumber,phone varchar...
AUniqueConstraintprohibits multiple rows from having the same value in the same column or combination of columns but allows some values to be null. The list of columns constrained by the UniqueConstraint is stored by column name. Nested Class Summary ...
Nonunique indexes permit duplicates values in the indexed column or columns. For example, the first_name column of the employees table may contain multiple Mike values. For a nonunique index, the rowid is included in the key in sorted order, so n...
select OWNER,CONSTRAINT_NAME ,COLUMN_NAME,POSITION from User_cons_columns where TABLE_NAME='EMP'; We will get null values for the Position column if we have a single column in the constraint. If there are multiple columns present in the constraints, Position will specify the order of the co...
Column_name, data_type, CONSTRAINT, constraint_name, UNIQUE If the unique constraint protects multiple data columns, then the unique constraint is added as a table constraint. Syntax as follows: CONSTRAINT, constraint_name (column), UNIQUE, USING, INDEX, TABLESPACE (tablespace_name), STORA...
unique indexes, 10-24 UNIQUE key constraints, 25-8 composite keys, 25-9, 25-11 constraint checking, 25-23 indexes used to enforce, 25-10 maximum number of columns, 25-10 NOT NULL constraints and, 25-11 nulls and, 25-11 size limit of, 25-10 unique keys, 1-57, 1-58...
alter table objects_table add constraint ot_pk primary key(object_id); begin dbms_stats.gather_table_stats( ownname => user, tabname => 'tables_table', method_opt => 'for columns size 60 owner' ); end; / set serveroutput off with driver as ( select /*+ materialize */ tt.owner,...
A check constraint can be used to enforce simple rules, such as that the value entered in a column must be within a range of values. The rule must be an expression which will evaluate to TRUE or FALSE. The rules can refer to absolute values entered as literals or to other columns in ...